With a Control Box for a Control Valve with Stepping Actuator it is possible to position the valve from 0 to 100% at any desired setting. This box is always used for a control valve which is unbalanced. In event of a shutdown, the solenoid valves will be de-energized and will cause the control valve to travel to the safe position at all time (Normally Close or Normally open). In case of loss of hydraulic power the valve will stay on latest position.
The hydraulic supply from an external source (e.g. HPU) at all time force the valve to go to safe situation, but with two solenoid valves and flow restrictions the valve can be opened or closed at a certain speed and set at the required position. The positioner on the valve will give feedback of the actual position of the control valve. Important is to have a comparison of the setting and feedback not 100% equal, otherwise the unit will respond very nervously and consume a lot of hydraulic fluid.